Hamill and Kevin Conroy are confirmed to reprise their respective voices for the roles of The Joker and Batman. Tara Strong will provide her voice for Barbara Gordon (Batgirl) and Ray Wise is set for Commissioner Gordon. Hamill said in a statement to Comic Book Resources:

"The chance to work once again with Kevin Conroy, my favorite Batman, in what some consider the definitive origin of this iconic villain is a dream come true for me. I am beyond thrilled to return as The Joker in 'The Killing Joke!'"

Batman: The Killing Joke will make its debut at this year’s upcoming San Diego Comic-Con. For those of you unable to attend, you'll be able to find the film in stores this summer.